Supercritical-Water-Cooled Reactor

Supercritical-Water-Cooled Reactor (SCWR) are high temperature, high-pressure, light-water-cooled reactors that operate above the thermodynamic critical point of water (374°C, 22.1 MPa).

The reactor core may have a thermal or a fast-neutron spectrum, depending on the core design. The concept may be based on current pressure vessel or on pressure tube reactors, and thus use light water or heavy water as moderator. Unlike current water-cooled reactors, the coolant will experience a significantly higher enthalpy rise in the core, which reduces the core mass flow for a given thermal power and increases the core outlet enthalpy to superheated conditions. For both pressure vessel and pressure-tube designs, a once through steam cycle has been envisaged, omitting any coolant recirculation inside the reactor. As in a boiling water reactor, the superheated steam will be supplied directly to the high pressure steam turbine and the feed water from the steam cycle will be supplied back to the core. Thus, the SCWR concepts combine the design and operation experiences gained from hundreds of water-cooled reactors with those experiences from hundreds of fossil-fired power plants operated with supercritical water (SCW). In contrast to some of the other Generation IV nuclear systems, the SCWR can be developed incrementally step-by-step from current water-cooled reactors.

Canada, Japan, Russia, Europe and China have supercritical water reactor designs.

The construction cost of SCWR plants has been targeted at $900/kW in the GIF Roadmap. This could be up to half the cost of reactors in China and over three times cheaper than reactors in the United States.

The Nuclear Power institute of China said it had identified four stages of development, continuing until 2025. Further technology development will begin this year, followed by engineering research and development from 2017-2021, construction from 2019 -2023, and commissioning between 2022 and 2025.

IAEA looked at SCWR

Other advantages

* Reactor coolant pumps are not required. The only pumps driving the coolant under normal operating conditions are the feed water pumps and the condensate extraction pumps.
* The steam generators used in pressurized water reactors and the steam separators and dryers used in boiling water reactors can be omitted since the coolant is superheated in the core.
* Containment, designed with pressure suppression pools and with emergency cooling and residual heat removal systems, can be significantly smaller than those of current water-cooled reactors.
* The higher steam enthalpy allows to decrease the size of the turbine system and thus to lower the capital costs of the conventional island.

Simplicity

* Significant reduction of number of components as compared to present-day pressure-tube reactors (steam generators, fuelling machine, inlet feeders and fuel channel end fitting internals are eliminated)
* Calandria vessel is low pressure. Hence, control and shutoff rods penetrate the low-pressure calandria, not a pressure vessel at a SC pressure.
* Supercritical coolant is not in contact with in-core pressure bearing components.
* Inlet plenum is at a temperature close to those in present-day PWR operating temperatures. Not a high-risk technology.
* Refueling, fuel channel inspection and fuel channel replacement activities are simpler, because fuel channels can be accesses simply by removing the head of the inlet plenum. There are no internal components or penetrations at the
inlet plenum.

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